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U.S. lawmakers from both parties expressed skepticism regarding a possible military strike on Syria following a 90-minute briefing held Thursday evening, with many feeling President Obama needs to make a better case for action, NBC News reports.

The focus of the unclassified briefing — which included Secretary of State John Kerry, Defense Secretary Chuck Hagel, and other intelligence and military officials — was to prove Syrian President Bashar al-Assad was guilty of using chemical weapons on Aug. 21. Senior administration officials have said they have "no doubt" the Syrian government was responsible for the alleged attack, reportedly resulting in about 3,600 injured and hundreds dead.

"They weren’t specific in terms of ‘Person A named so-and-so did this and said that,'" Rep. Eliot Engel (D-N.Y.), ranking member of the House Foreign Affairs Committee, told NBC. "They just said that they had intercepted communications talking about doing this.”

The timing of the briefing came roughly 30 minutes after the British parliament had voted against military intervention in Syria — delivering an embarrassing blow to the legitimacy of U.K. Prime Minister David Cameron.

Many top Democrats stood by Obama and offered support for military action after the briefing, although a significant number opted to join Republicans in calling for a vote before any action. In addition to wanting a vote, Speaker John Boehner (R-Ohio) has asked that 14 specific questions be answered before supporting any strike.

“It’s a very tough situation with no good options," Rep. Howard "Buck" McKeon (R-Calif.), chairman of the House Armed Services Committee, told NBC. “It’s up to the president to sell this to the American people.”

The U.S. has maintained that any action would be limited in scope — designed to send a message to Assad, but intended to avoid continued military action (such as boots on the ground). A limited strike hinges on three conditions, according to The Washington Post:

...completion of an intelligence report assessing Syrian government culpability in last week’s alleged chemical attack; ongoing consultation with allies and Congress; and determination of a justification under international law.

Besides trying to sway congressional leaders, Obama will likely try to present a stronger case to the American people soon, with the release of a completed intelligence report to be made public Friday, reports CBS' Major Garrett.

"He believes that there are core interests at stake for the United States and that countries who violate international norms regarding chemical weapons need to be held accountable," said White House spokesman Caitlin Hayden in an email.